The aim of the study was to focus on important aspects and issues associated with bi-level positive airway pressure (BPAP) mask treatment in acute exacerbation of chronic obstructive pulmonary disease based on the experiences of patients and nurses. The study has a qualitative design with a phenomenological approach. The data are based on qualitative in-depth interviews with five patients who had used BPAP-mask treatment intermittently over several days in the acute stages and a focus group with eight experienced nurses from a specialized unit in a Norwegian university hospital. The data have been analysed on the basis of Amadeo Giorgi's phenomenological method. Findings are discussed in the light of the Norwegian philosopher Kari Martinsen's nursing philosophy with practical implications. The essential structure of being treated with BPAP-mask from the patients' point of view may be characterised as a feeling of being trapped in a situation of complete dependence on others, combined with a will to mobilize inner strength. The essential structure is presented through three themes describing the patient's lived experience: Anxiety, panic and loss of control, regaining control and trust through skilled help, and a mobilization of willpower. The nurses' experiences point to the challenges related to individual needs, ethics, technical, medical and relational competence in addition to constraints on time. The study concludes that mask treatment can be a traumatic experience for the patients. The interplay between dependence and autonomy in the patient's interaction with health care providers, such as deciding when to take breaks, getting enough sleep, mobilizing inner strength and establishing trust and security are important factors in coping with the mask. Clinical competence, the ability to articulate impressions, and sufficient time on the part of health workers are other aspects that can be decisive to how well the patient tolerates BPAP-mask treatment.